Susceptibility to climate change differs across sectors and regions. A clear
example is sea-level rise, which mostly affects coastal zones (see Box
19-2). People living in the coastal zone generally will be negatively affected
by sea-level rise, but the numbers of people differ by region. For example,
Nicholls et al. (1999) found that under a sea-level rise of about 40 cm by the
2080s, assuming increased coastal protection, 55 million people would be flooded
annually in south Asia; 21 million in southeast Asia, the Philippines, Indonesia,
and New Guinea; 14 million in Africa; and 3 million in the rest of the world.
The relative impacts in small island states also are significant (see Section
19.3). In addition, the Atlantic coast of North and Central America, the
Mediterranean, and the Baltic are projected to have the greatest loss of wetlands.
Inland areas face only secondary effectswhich, unlike the negative primary
effects, may be either negative or positive (Yohe et al., 1996; Darwin and Tol,
2001).

Box 19-3. The Impact of Climate Change on Agriculture

The pressures of climate change on the world's food system are better
understood than most other impacts. Research has focused on crop yields;
on the basis of those insights, many studies also look at farm productivity,
and a smaller number look at national and international agricultural markets.

Climate change is expected to increase yields at higher latitudes and
decrease yields at lower latitudes. Changes in precipitation, however,
also can affect yields and alter this general pattern locally and regionally.
Studies of the economic impact of this change (in all cases, climate change
associated with 2xCO2) conclude that the aggregated global
impact on the agricultural sector may be slightly negative to moderately
positive, depending on underlying assumptions (e.g., Rosenzweig and Parry,
1994; Darwin, 1999; Parry et al., 1999; Mendelsohn et al., 2000). Most
studies on which these findings are based include the positive effect
of carbon fertilization but exclude the negative impact of pests, diseases,
and other disturbances related to climate change (e.g., droughts, water
availability). The aggregate also hides substantial regional differences.
Beneficial effects are expected predominantly in the developed world;
strongly negative effects are expected for populations that are poorly
connected to regional and global trading systems. Regions that will get
drier or already are quite hot for agriculture also will suffer, as will
countries that are less well prepared to adapt (e.g., because of lack
of infrastructure, capital, or education). Losses may occur even if adaptive
capacity is only comparatively weak because trade patterns will shift
in favor of those adapting best. Overall, climate change is likely to
tip agriculture production in favor of well-to-do and well-fed regionswhich
either benefit, under moderate warming, or suffer less severe lossesat
the expense of less-well-to-do and less well-fed regions. Some studies
indicate that the number of hungry and malnourished people in the world
may increase, because of climate change, by about 10% relative to the
baseline (i.e., an additional 80-90 million people) later in the
21st century (e.g., Parry et al., 1999).

Agriculture, to turn to another example, is a major economic
sector in some countries and a small one in others. Agriculture is one of the
sectors that is most susceptible to climate change, so countries with a large
portion of the economy in agriculture face a larger exposure to climate change
than countries with a lower share, and these shares vary widely. Whereas countries
of the Organisation for Economic Cooperation and Development (OECD) generate
about 2-3% of their GDP from agriculture, African countries generate 5-58%
(WRI, 1998).

Activities at the margin of climatic suitability have the most to lose from
climate change, if local conditions worsen, and the most to win if conditions
improve. One example is subsistence farming under severe water stressfor
instance, in semi-arid regions of Africa or south Asia. A decrease of precipitation,
an increase in evapotranspiration, or higher interannual variability (particularly
longer droughts) could tip the balance from a meager livelihood to no livelihood
at all, and the unique cultures often found in marginal areas could be lost.
An increase in precipitation, on the other hand, could reduce pressure on marginal
areas. Numerous modeling studies of shifts in production of global agricultureincluding
Kane et al. (1992), Rosenzweig and Parry (1994), Darwin et al. (1995), Leemans
(1997), Parry et al. (1999), and Darwin (1999)have estimated that production
in high-latitude countries is likely to increase and production in low-latitude
countries is likely to decrease, even though changes in total global output
of agriculture could be small. Results in the temperate zone are mixed. Low-latitude
countries tend to be least developed and depend heavily on subsistence farming.
Under current development trends they will continue to have a relatively high
share of GDP in agriculture. Thus, the impacts of declines in agricultural output
on low-latitude countries are likely to be proportionately greater than any
gains in high-latitude countries (see Box 19-3).

Vulnerability to the health effects of climate change also differs across regions
and within countries, and differences in adaptive capacity again are important.
Box 19-4 notes that wealthier countries will be better
able to cope with risks to human health than less wealthy countries. Risks also
vary within countries, however. In a country such as the United States, the
very young and the very old are most sensitive to heat waves and cold spells,
so regions with a rapidly growing or rapidly aging population would have relatively
large exposure to potential health impacts. In addition, poor people in wealthy
countries may be more vulnerable to health impacts than those with average incomes
in the same countries. For example, Kalkstein and Greene (1997) found that in
the United States, residents of inner cities, which have a higher proportion
of low-income people, are at greater risk of heat-stress mortality than others.
Differences among income groups may be more pronounced in developing and transition
countries because of the absence of the elaborate safety nets that developed
countries have constructed in response to other, nonclimate stresses.

These observations underscore one of the critical insights in Chapter
18: Adaptive capacity differs considerably between sectors and systems.
The ability to adapt to and cope with climate change impacts is a function of
wealth, technology, information, skills, infrastructure, institutions, equity,
empowerment, and ability to spread risk. The poorest segments of societies are
most vulnerable to climate change. Poverty determines vulnerability via several
mechanisms, principally in access to resources to allow coping with extreme
weather events and through marginalization from decisionmaking and social security
(Kelly and Adger, 2000). Vulnerability is likely to be differentiated by genderfor
example, through the "feminization of poverty" brought about by differential
gender roles in natural resource management (Agarwal, 1991). If climate change
increases water scarcity, women are likely to bear the labor and nutritional
impacts.

The suggested distribution of vulnerability to climate change can be observed
clearly in the pattern of vulnerability to natural disasters (e.g., Burton et
al., 1993). The poor are more vulnerable to natural disasters than the rich
because they live in more hazardous places, have less protection, and have less
reserves, insurance, and alternatives. Adger (1999), for instance, shows that
marginalized populations within coastal communities in northern Vietnam are
more susceptible to the impacts of present-day weather hazards and that, importantly,
the wider policy context can exacerbate this vulnerability. In the Vietnamese
case, the transition to market-based agriculture has decreased the access of
the poor to social safety nets and facilitated the ability of rich households
to overexploit mangroves, which previously provided protection from storms.
Similarly, Mustafa (1998) demonstrates differentiation of flood hazards in lowland
Pakistan by social group: Insecure tenure leads to greater impacts on poorer
communities. See Chapter 18 for further examples. The
natural disaster literature also concludes that organization, information, and
preparation can help mitigate large damages at a moderate cost (e.g., Burton
et al., 1993). This underscores the need for adaptation, particularly in poor
countries.

Box 19-4. The Health Impacts of Climate Change

Global climate change will have diverse impacts on human healthsome
positive, most negative. Changes in the frequency and intensity of extreme
heat and cold, floods and droughts, and the profile of local air pollution
and aeroallergens will directly affect population health. Other effects
on population health will result from the impacts of climate change on
ecological and social systems. These impacts include changes in infectious
disease occurrence, local food production and nutritional adequacy, and
the various health consequences of population displacement and economic
disruption. Health impacts will occur very unevenly around the world.
In general, rich populations will be better protected against physical
damage, changes in patterns of heat and cold, introduction or spread of
infectious diseases, and any adverse changes in world food supplies.

The geographic range and seasonality of various vector-borne infectious
diseases (spread via organisms such as mosquitoes and ticks) will change,
affecting some populations that currently are at the margins of disease
distribution. The proportion of the world's population living in
regions of potential transmission of malaria and dengue fever, for example,
will increase. In areas where the disease currently is present, the seasonal
duration of transmission will increase. Decreases in transmission may
occur where precipitation decreases reduce vector survival, for example.

An increased frequency of heat waves will increase the risk of death
and serious illness, principally in older age groups and the urban poor.
The greatest increases in thermal stress are forecast for mid- to high-latitude
(temperate) cities, especially in populations with limited air conditioning.
Warmer winters and fewer cold spells, because of climate change, will
decrease cold-related mortality in many temperate countries. Basic research
to estimate the aggregate impact of these changes has yet been limited
largely to the United States and parts of Europe. Recent modeling of heat-wave
impacts in 44 U.S. urban populations, allowing for acclimatization, suggests
that large U.S. cities may experience, on average, several hundred extra
deaths per summer. Although the impact of climate change on thermal stress-related
mortality in developing country cities may be significant, there has been
little research in such populations.

For each anticipated adverse health impact, there is a range of social,
institutional, technological, and behavioral adaptation options that could
lessen that impact. The extent to which health care systems will have
the capacity to adopt them is unclear, however, particularly in developing
countries. There is a basic and general need for public health infrastructure
(programs, services, surveillance systems) to be strengthened and maintained.
The ability of affected communities to adapt to risks to health also depends
on social, political, and economic circumstances.